A. Field of the Invention
The present invention relates to systems for topically heating or cooling an animal or human body. The invention more particularly concerns such a system in which a heating or cooling liquid is circulated in a hermetically sealed flow path between a heating or cooling device and a heating or cooling pad. In an especially preferred form, the flow path includes a cassette or similar cartridge which is engageable with a pump and a heating or cooling unit. The flow path is permanently sealable and precludes a need for joints, couplings or similar fluid connectors for assembling and disassembling the flow path.
B. The Prior Art
Localized hyperthermia or hypothermia (topical application of heat or cold, respectively, to selected regions of the body) is used to treat a wide variety of medical/surgical conditions in hospitals, nursing homes, and other care giving locations and is becoming increasingly important in areas such as home health care and sports medicine. Thrombophlebitis, cellulitis, decubitus ulcerations, incisional pain and swelling, post-partum and post-operative pain and swelling, muscle pathology and pain, and joint pathology and pain are some common medical/surgical conditions for which localized hypothermia or hyperthermia can be an effective adjunctive therapy.
Techniques that deliver localized hypothermia or hyperthermia can be classified as moist or dry. With the moist technique, a hydrated surface is in direct or indirect contact with the body; with the dry technique, a dry surface is in direct or indirect contact with the body. Devices that deliver localized hypothermia or hyperthermia can be characterized as continuous or intermittent. They may be referred to generically as thermiatric devices or units. Continuous devices draw their energy from various types of electrical power sources. Intermittent devices typically draw their energy from anything buy electrical power sources, i.e., exothermic/endothermic and chemical systems.
Localized, heat transfer devices known to those of skill in the art include simple devices, such as hot-water bottles and ice packs, as well as somewhat more sophisticated electromechanical systems.
One commercially available single use system comprises an enclosed rupturable membrane separating two or more chemicals. The application of pressure to the membrane causes it to rupture, allowing the chemicals to mix in an endothermic or exothermic reaction. The net effect is a bag that absorbs heat from or adds heat to the body. Although this system can be effective and practical when localized short-term cooling or heating of the body is desired, it is not reusable and does not deliver constant uniform controlled heating and cooling.
The electrical heat lamp is another system used to add heat to a specific region of the body. Although many commercially available heat lamps have electrical systems that allow one to control the intensity of the light bulb and thereby control temperature, those systems are cumbersome and do not deliver uniform or site specific controlled heating.
More complicated systems require assembly and comprise a flexible polymeric applicator pad which has an inlet port and an outlet port. The ports must be reversibly connected, through a series of individual tubes, to a central fluid reservoir located in a separate housing. With these systems, the housing will contain a mechanism for heating or cooling the fluid in the reservoir and for circulating the fluid through the reservoir and into the applicator pad. For example, U.S. Pat. No. 4,459,468 describes an electromechanical controlled-temperature fluid circulating system designed for assembly to and use in reversible combination with a flexible thermal blanket or pad. This type of system comprises a fluid reservoir, heat transfer elements, temperature control circuitry, power supply, pump, and inlet and outlet ports reversibly connected to two flexible tubes that, in turn, connect the system to the pad. The reservoir contains a fluid, usually water, that can be heated or cooled by the heat transfer elements disposed within or adjacent the reservoir. The temperature of the fluid is monitored by the temperature control circuitry, which, in turn, is electrically connected to thermal modules that can be activated to maintain a desired fluid temperature. A pump is connected between the reservoir and the inlet and outlet ports. The inlet and outlet ports much be connected to two tubes for transferring fluid to an additional set of ports, disposed in the separate flexible applicator pad. The system must be reversibly assembled prior to use by coupling the pad to the two tubes, which are in turn connected to the ports in the housing containing the reservoir and pump.
A system described in U.S. Pat. No. 3,967,627 also has a fluid reservoir or standpipe, which is vented to the atmosphere, a heat exchanger with control circuitry, a peristaltic pump, and inlet and outlet ports. With this system, the heat transfer fluid is stored and maintained in the vented reservoir, and a peristaltic pump is used to force the fluid to flow through a heat exchanger, where the fluid temperature is sensed and regulated, to the outlet port. For assembly, the latter may be reversibly connected to a tube which may be reversibly connected to yet an additional port located in the applicator pad. As with the device set forth in U.S. Pat. No. 4,459,468, the system must be reversibly assembled prior to use by coupling the pad to conduits, which are in turn connected to the ports in the housing.
It can readily be seen that with devices of the types described above, the applicator pad is initially fluidless and, when the pad is not is use, the inlet and outlet ports are open to the atmosphere, preventing maintenance of sterile conditions within the pad. When one desires to use the pad, the ports must be reversibly coupled to a pair of intermediate conduits. The conduits are, in turn, reversibly connected to another pair of ports mounted on the housing.
Such systems are inefficient, messy, and in some cases hazardous to use. First, the reversible coupling of the applicator pad to the fluid circulating system is cumbersome and time consuming. The devices have multiple fluid couplings, which must be manually connected and often leak, thereby preventing one from maintaining the circulating fluid as sterile. Inexactly fitted connections result in fluid leakage at the couplings, for example, between the inlet and outlet ports of the applicator pad and the intermediate tubing and between the tubing and the ports leading to the fluid reservoir. Additionally, when the system is disassembled after use, additional fluid leaks from the applicator pad and the intermediate tubing that connects the fluid circulating system to the applicator pad. This leakage increases the potential for electrical shock and spread of disease, particularly nosocomial infections, as contaminated fluid leaks onto the patient's bed or body parts to which the pad is applied, often a recent surgical wound. It also reduces the volume of fluid in the reservoir and, in conjunction with the venting, necessitates frequent refilling of the fluid reservoir.
Second, the efficiency of systems having vented reservoirs and orientation dependent pumps is contingent on the proper placement of the fluid circulating system relative to the applicator pad. If the elevation of the fluid circulating system is the same as that of the applicator pad, the systems may function normally. However, as the difference between the elevation of the fluid circulating system and the elevation of the applicator pad increases, the efficiency of the system decreases. Moreover, because the reservoirs are vented, any tilting of the fluid circulating system may cause fluid to leak or spill. Fluid can also evaporate from the vented reservoir; hence, the fluid level requires constant monitoring in order to allow one to maintain the proper level of circulating fluid for safe operation of the unit. Finally, the vent facilitates contamination of fluid in the reservoir.
Finally, non-sterility of fluids in the reservoir and the difficulty or impossibility of cleaning or sterilizing reusable parts of the device may induce the spread of nosocomial infection, already a serious problem in most hospitals. Infectious pathogenic microorganisms (for example, those of the Pseudomonas and Staphylococcus species) can enter and proliferate within the system and, most often, in the reservoir. Exposure of surgical, traumatic, or pathologic wounds to these pathogens by fluid that leaks from fluid couplings, failed seams in the reservoir or applicator pad, or from the vented reservoir itself, may contribute to the development of secondary infection in the individuals exposed.
The applicator pads used in connection with such devices, for example those described in U.S. Pat. Nos. 3,867,939, 4,114,620, and 4,149,541, also have a number of disadvantages. The most commonly used applicator pads are constructed of flexible polymeric sheeting, formed into conduits for fluid passage. More specifically, U.S. Pat. No. 3,867,939, describes a widely used disposable applicator pad for medical application. The pad is of a laminate construction, with outer layers of absorbent material bonded to a polymeric inner layer that forms a conduit for the passage of fluid. Because of the design of this pad, a moist or dry technique can be used when therapy is delivered. However, if the pad is soiled with urine, blood, or other substances, it must be replaced with a clean, new pad since the integral absorbent coverings are not designed to be cleaned or removed. U.S. Pat. Nos. 4,114,620 and 4,149,541 also relate to polymeric laminated applicator pads that contain internal conduits for fluid passage. Although these applicator pads are more easily cleaned than those described above, they are uncomfortable for the patient, may contribute to skin irritation and cannot be used for moist heat transfer.
From the discussion above, it is apparent that substantial improvement is needed in localized heat or cold transfer devices and applicator pads designed for use in conjunction with such devices. Moreover, the problems described above are not exhaustive. Instead, they are merely examples of difficulties encountered with present devices. Clearly, a new and superior heat transfer device is greatly needed.